A common oil well pumping system includes a reciprocating pump cylinder lowered into the well with a pump rod extended to the surface within tubing. The pumping unit at the surface includes the walking beam mounted upon horizontally-axised, transverse pivot at the top of a sampson post with one end being connected to the pump rod and the other end being connected to the crank of a drive motor through a connecting rod. Rotation of the crank cause the walking beam to rock or oscillate in a vertical plane to raise and lower the pump rod. The connection of the connecting rod to the crank is adjustable to change the rock of the walking beam of the pump. The rod-connected end of the walking beam is provided with the familiar "horse head" to keep the pump rod in alignment with the well axis. The opposite end of the walking beam carries a counterbalance weight to offset the weight of the pump rod and minimize the stress on the motor.
When pumping an oil well, both oil and gas may be produced and the capture of the gas is profitable. Where a high-pressure, high-volume gas flow exists, the gas can be added to a distribution system by a direct line connection or if the pressure is less than the distribution system pressure, a booster compressor can be used. On small volume gas wells, a compressor is used to lower casing head pressure to increase oil production.
Former oil production practice was to waste this gas as by flaring, but his is not always done today because of environmental considerations and the gas has become valuable. To capture and compress such small amounts of low-pressure gas, a simple cylinder-type gas compressor, hereinafter sometimes referred to as a "compressor cylinder", is mounted on the frame pumping unit with the piston rod thereof being connected to the walking beam. The rocking of the walking beam reciprocates the piston to effect intake and compression strokes. A gas intake line from the well head to the base of the cylinder, a discharge line from the cylinder to a distribution system line and suitable check valves in the intake and discharge lines complete the basic system.
The location and position of this compressor cylinder on the pumping unit must be carefully selected so as to produce the necessary gas pressure. The cylinder of the pumping unit and the connection point of its piston rod on the walking beam must be such as to place the cylinder in an upright position and normal to the walking beam when the beam is at an intermediate substantially-horizontal position. This location must also be such that the rocking movement of the walking beam at the connection point is less, and preferably only slightly less, than the maximum stroke of the piston within the cylinder. Finally, the position of the base of the cylinder on the pumping unit frame must be such that the piston moves closely to the bottom of the cylinder at the completion of the compression stroke to produce the rated gas pressure and to move all compressed gas out of the cylinder and into the discharge line. This is necessary to prevent wasted movement of the piston due to gas expansion, especially where the gas pressure during the intake stroke is low or even sub-atmospheric.
To properly locate the cylinder to take into account the factors above mentioned it has been the practice to build a base mount on the frame of the pumping unit. Such a mount is a welded framework at a suitable location as adjacent to the sampson post opposite to the well head. Once so mounted the cylinder operates properly and satisfactorily as long as the same pumping operation continues. However, the conditions in a well will not always remain the same. The amount of oil which can be pumped can vary and pressures in the well, primarily the gas pressure, can also vary. To accommodate these variations it is necessary to adjust the stroke of the walking beam for the oil and to adjust the position of the gas compressor pump in relation to the walking beam. The walking beam adjustment is effected by changing the throw of the drive motor crank. Such an adjustment changes the piston movement of the gas compressor cylinder, and it becomes necessary to relocate the cylinder with respect to the pumping unit frame and the walking beam. To do this, an operator will need to change and/or relocate the base mount. Cutting and welding torches will be necessary and this can be a major job.